Sonnax 34200-01K Boost Valve Kit for GM Transmission - 4L80-E 4L85-E

The Sonnax 34200-01K boost valve kit is designed to solve common problems in GM 4L80-E and 4L85-E automatic transmissions, including uncontrollable line pressure rise (up to 500-600 psi), high line pressure in reverse, buzzing noises, and broken direct clutch drums or cases. These issues are typically caused by reverse boost oil entering the torque signal circuit due to wear-created cross leaks at the sleeve and oil leakage past the aluminum balance plug.

Key Features:

• Hardened steel boost valve with over 20% wider spools provides better durability and increased sealing contact area
• Annular grooves on boost valve spools reduce side loading that causes wear
• Quality steel boost sleeve with external O-rings provides positive seal to compensate for pump cover bore wear
• Includes replacement aluminum balance oil plug with O-ring to ensure proper sealing and adequate back pressure on the pressure regulator valve
• O-ring style kit can be retrofitted back to 1989 models

Kit Includes:

• Hardened steel boost valve
• Steel boost sleeve
• Two sleeve O-rings
• Aluminum balance plug
• Balance plug O-ring

This comprehensive valve kit restores hydraulic integrity and eliminates pressure-related failures in 4L80-E and 4L85-E transmissions. Compatible with 1989 and later GM 4L80-E and 4L85-E automatic transmissions.